Device for converting electric oscillations into mechanical vibrations



Sept. 1, 1931. G. HOLST ET AL 1,320,943

DEVICE FOR CONVERTING ELECTRIC OSCILLATIONS INTO MECKAKICAL VIBRATIONS File'c'l Dec. 16, 1927 Bil/ 1, i

INVENTOR AREND 1. VAN unx BY ROELOF VERMEULEN GILLES HOL (/9 ,da M

ATTO EY ifPatented Sept." 1, 1931 I GILLES UNITED STATES PATENT OFFICE OF DELAWARE HOLST, ABEND THOMAS VAN URK, AND ROELOF VERMEULEN, NETHERLANDS, ASSIGNORS TO RADIO CORPORATION OF AMERICA,

or EINDHOVEN, a. coarom'rron DEVICE FOR CONVERTING ELECTRIC O'SCILLATIONS INTO MECHANICAL 'VIBRA'IIONB Application tiled December 16, 1927. Serial No. 240,571, and in ,the'NetherlandS February 18, 1927.

This invention is concerned with a device such as is used in telephones, loudspeakers and the like for converting electric oscillations into mechanical vibrations.

According to the invention a ferromagnetic element, i. e., an armature, which is adapted to be subjected to the influence of electric oscillations, is arranged so as to move within and in the direction of two parallel but opposite magnetic fields. The armature is supported by having its ends secured to a resiliently mounted frame.

It is easier to support the frame than to support the armature and the frame is also more accessible which permits the springs to I be arranged at any point and in any number desired. If the frame .is moved in a determined manner the armature is forced by the stiff construction of the frame to move in the same manner and vice versa. The probabiliv ty of the armature receiving, in addition to said movement n a determined direction, another movement about its own axis is therefore negligible because of such rigid construction but it constitutes a source of danger in devices in which the ends of the armature 'are each directly secured to a spring support because the freedom of moveown axis.

ment of the armature is thus increased.

According to the present invention the frame may be rectangular in form with the armature connected to two parallel sides of the frame, the middles of the other two sides being secured to the spring supports.

If the frame-is supported by unilaterally clamped springs the points of clamping of the springs'may be located on the same side relatively to the axis of movement of the ar-' mature. The springs being caused to proceed in the same direction as the armature, the latter will receive a substantially rectilinear movement but will not move about its If the springs are clamped unilaterally the restoring force exerted by them will proceed in line with the deviation of the armature. The magnetic force is known to change quadratically to this deviation so that the resultant repulsive force is not proportional to the deviation of the armature. If, however, the

armature is caused to move through very small distances, substantially proportionate resultant forces will ensure through the said distances.

The loudspeaker may be particularly sensitive when the springs are very slack which however entails the probability that the armature will come, into contact with and adhere to the magnet.

According to the invention the frame has fixed to it one or more wires or chords which prevent the armature from receiving any-undesirably great movement and from contacting with the poles.

The accompanying drawings illustrate a construction embodying the invention. In the said drawings:

Figure 1 is a side view of a magnet system embodying the invention.

Figure 2 IS a section taken on the line 11-11 of Figure 1.

Figure 3 is a section 111-411 of Figure 1.

Figure 4 is a slightly different construction embodying the invention. I

Figure 5 represents graphically the forces acting on the armature at different deviations in the construction shown in Figure 1.

Figure 6 shows graphically the forces acting on the armature in'the construction of Figure 4.

Figure 7 illustrates a modification of the means for applying a restoring force tothe armature. The magnet system is constituted by a permanent magnet 1 to which pole pieces 2 and 3 are attached. The pole pieces are shaped so as to form two air gaps providing two partaken on the line allel but oppositely directed magnetic fields,

to the arrangement of the is shown in Figure 5.

placement a'the force exerted The frame has secured to it a stud 5 which may be connected directly to an oscillating member such as a loudspeaker diaphragm.

The function of the magnet system is as follows:

A magnetic flux will be induced in the armature by the electrical current passing through the coil, said flux resulting, owing poles, in a movement of. the armature in a direction determined by the magnetic field. The movement thus received by the armature will be a function of the magnetic force of the fixed magnets and that due to the polarization of the armature and of the acting force of the "sprin s 8. The magnitude of these forces for different displacements of the armature The abscissas designate the movement of the armature from its central position, the

ordinates the forces exerted on the armature. In its central position the armature will be attracted at equal force by the north and south poles so that the forces exerted upon the armature by the magnetic field are equal to zero. I

The armature is in a critical state of equilibrium as even the slightest displacement brings about a force in the direction of the nearest pole of the magnet. The magnetic force is known to change in a manner inversely proportional'to the square of the distance between pole and armature so that the curve which represents the forces at any displacement from the center will be para-.

bohcm form. a b III; the drawings this curve is designated The curve A represents the extent of the restoring forces exerted by the s rings 8. These springs being clamped unilaterally the curve of the variation in the forces will linear.

It is evident from Figure 5 that at the disby the permanent magnet is equal to the reaction force of the spring so that at a little added dis-- placement in the direction of the pole the .magnetic force overcomes the .reactive force an t he armature races and will adhere to this pole. At slight displacements, however, for example at those smaller than the displacement b, there will not be this probability and the resultant directing force will be about proportional to the deviation of the armature (see the cross-hatched piece). However, it will always be necessary to use a com aratively stiff spring in order to prevent t e armature adhering to the poles.

In Figure 4 a construction is shown in which the sprin 8 are very slack or resilient so that the orce exerted by the springs increases upon displacement of'the armature as designated in Figure 6 by A In this figure B again representsthe force exerted by the permanent magnet. This results immediatel To overcome this ob'ection, each of the points -10 and 10' of the rame 7, see Figure 4, is connected by means of chords or wires 15 to fixed points 16 and 17. I

As shown in Fig. 7, these wires or chords 15 are not tautly stretched and only come into operation when the armature has reccived a determined displacement. Thus, for example, in the case of displacement superior to c (Figure 6) the restoring force (line A.) will be reinforced by the tension of the wire (line C so that theline A shows a deviation D at the point d which shifts the danger point of the magnetic forces overcoming the reactive spring forces to the displacement e."-. The fi ure shows that for small dis lacements suc 1 as b the force to be applied to secure displacement is comparatively small so that the system is highly sensitive. In the case of greater displacements this sensitivencss will continue since the directing force rc uired increases by very small values.

Vhat we claim is:

l. A device for converting electrical oscillations into mechanical vibrations comprising an element having a normal'position ofequilibrium and adapted tomove therefrom 1n response to said electrical oscillations,-

spring means for supporting said element, additlonal spring means not operatively associated with said element at its normal position of equilibrium, and means for operatively associating said addltidnal spring means with said element after said element has moved a predetermined distance from its field, a stationary coil surrounding'said,

armature for carrying the electrical oscillations, said coil bein adapted to polarize said armature in accordance with the electrical oscillations passing through the coil, a spring supporting said armature, and an additional spring for influencing the movement of the armature after a predetermined displacement of said armature from its position of equilibrium, said additional spring having no influence on the movement of said arma-' ture until it has moved the predetermined distance.

3. A device for converting electrical oscillations into mechanical vibrations comprisported in the magnetic field of said permanent magnet and adapted to move in said field, a stationary coil surrounding said armature for carrying the electrical oscillations, said coil being adapted to polarize said armature in accordance with the electrical oscillations passing through the coil, a spring for restoring said armature to its position of equilibrium, additional spring means inoperatively associated with said armature in its position of equilibrium, and means for operatively connecting said additional spring means with said armature after a predetermined displacement of the armature from its position of equilibrium.

4. A device for converting electrical oscillations into mechanical vibrations comprising a permanent magnet, an armature, a frame supporting said armature in the magnetic field of said permanent magnet, a stationary coil surrounding said armature for carrying the electrical oscillations, said coil mg a permanent magnet, an armature supported in the magnetic'field of said magnet in a position 'ofequilibrium, a stationary coil surrounding the armature for carrying the electrical oscillations, said 'coil being adapted to polarize said armature in accord- 1 ance with the electrical oscillations passing through the coil whereby said armature is moved from its position of equilibrium, means for restoring said armature to its position of equilibrium, and additional means for influencing the movement of the armature only after a predetermined displacement of the armature from its position of equilibrium.

6. A device for converting electrical oscillations into mechanical vibrations comprising a permanent magnet, an armature, a frame supporting said armature 1n a position of equilibrium in the magnet field of said magnet, a stationary coil surrounding the armature for carrying the electrical oscillations, said coil being adapted to polarize said armature to produce motion thereof in accordance with the electrical oscillations passing through the coil, means associated with said frame for restoring said armature to lations, said coil being adapted to polarize said armature in accordance with the electri cal oscillations passing through the coil, fiat springs for supporting. said armature in its position of equilibrium, said fiat springs being fixed to a rigid support at one end and to said frame at theother end, additional springs normally having no influence upon said armature, and means for connecting said additional springs to said frame to influence the movement of the armature after a predetermined displacement of the armature from its position of equilibrium.

8. A device for converting electric oscillations into mechanical vibrations comprising a ferromagnetic element, means for subjecting said element to the electromagnetic influence of the electric oscillations, means for providing two parallel but oppositely directioned magnetic fields, a frame for positioning said element in the magnetic fields, and resilient means secured to said frame for supporting said frame for movement substantially parallel to the directions of said magnetic fields.

. 9. A device according to claim 8 characterized in that the frame consists of a rectangle, two parallel sides of which are connected by the element, and the midpoints of the other two, sides of which are secured to the resilient means. i

10. A device according to claim 8 in which the frame is supported by unilaterally 11o clamped springs, characterized in that the clamping points of the springs are located on the same side of the frame relativeto the axis of movement of the element and frame.

.11. A device according to claim 8 in which the springs are slack, characterized in that the frame has secured to it one or more spring-like members which prevent an undesirably great deviation of the element from its position of equilibrium upon movement therefrom, additional means for applying a its central position. 12o

GILLES HOLST. .AREND THOMAS vAN URK. ROELOF VERMEULEN. 

